# A student carries out oxidation reactions on two unknown organic compounds, X and Y. Compound X is oxidised by acidified potassium dichromate(VI) solution, producing a compound that gives a positive result with Tollens' reagent. Compound Y is also oxidised by acidified potassium dichromate(VI) solution, but the product does not react with Tollens' reagent. Identify the functional group present in each compound and explain what these observations tell us about the structure of each compound and the products formed.

> WJEC A-Level Chemistry (Wales) — 4.4 Aldehydes and ketones · Explain · 5 marks

> Acidified potassium dichromate(VI) solution is an oxidising agent commonly used in organic chemistry. Tollens' reagent produces a silver mirror when reduced by an aldehyde.

## Mark scheme (5 marks)

1. Compound X contains an aldehyde group (–CHO) / is an aldehyde
2. Compound X is oxidised to a carboxylic acid, which gives a positive result with Tollens' reagent because aldehydes (and their oxidation products) can be further oxidised / the aldehyde intermediate reacts with Tollens' reagent reducing silver ions to silver
3. Compound Y contains a ketone group (C=O flanked by two carbon groups) / is a ketone
4. Ketones cannot be oxidised to produce an aldehyde or carboxylic acid under these conditions (they resist further oxidation), so the product does not react with Tollens' reagent
5. The key structural difference is that aldehydes have a hydrogen atom bonded to the carbonyl carbon (–CHO), whereas ketones have two carbon groups bonded to the carbonyl carbon, which explains the difference in reactivity with Tollens' reagent

## Key terms

- [Tollens' reagent](https://www.gradenine.co.uk/glossary/tollens-reagent)
- [oxidation](https://www.gradenine.co.uk/glossary/oxidation)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-oxidation-reactions-03d781aa) · Published by Druglandscape Ltd.